this may seem silly but it’s very important. my knees and joints are wrecked cuz i didn’t do any of these things, so don’t be like me.
first off, whether you’re sitting in a chair or on a bed the most important thing is posture! check you aren’t slouching regularly, and if your seating arrangement doesn’t have back support, use pillows!!! especially for lumbar support, pillows are the best.
second, be aware of your legs! if you’re in a chair, the best way to sit is with your feet planted flat on the ground (or a foot rest if you don’t reach). if sitting on a bed, extend your legs forward and put a pillow under your knees. criss cross is fine too, but not for extended periods!
and finally, just some general advice, stretch everyday!!!!!! even if just for 5 minutes a day, it will make a monumental difference.
i hope this helped :D